1. Field of the Invention
This invention pertains to variable capacity refrigeration and heating systems and more particularly to control systems for controlling the capacity of such systems.
2. Description of the Prior Art
Absorption type refrigeration systems for chilling a fluid medium which may then be used to provide refrigeration to any desired location are well known. Typically, such systems are controlled by providing a temperature sensor which senses the temperature of the fluid medium either as it enters or leaves the evaporator. The signal from this sensor is then used to control the capacity of the refrigeration system in accordance with the load requirements. In an absorption type refrigeration system, this is accomplished by controlling the concentration of the refrigerant-absorbent solution supplied to the absorber.
Other control systems, such as those disclosed in U.S. Pat. Nos. 3,099,139 and 3,250,084 employ two separate temperature sensors, one disposed to sense the temperature of the fluid medium entering the refrigeration system and another to sense the temperature of the fluid medium after it has been cooled by the refrigeration system. However, these control systems, as well as the other prior art control systems known to applicant, are only adapted to vary the refrigeration capacity of the system in response to varying load conditions and not in response to changes in the internal conditions in the refrigeration system itself. Thus, when there is a malfunction in the refrigeration system, such as fan breakage, fouling, accumulation of noncondensibles, etc., prior art control systems normally result in maximum energy input to the refrigeration system as they attempt to compensate for the malfunction. Thus, these control systems are extremely inefficient from a fuel consumption point of view.
Other exemplary refrigeration control systems are disclosed in U.S. Pat. Nos. 3,661,200; 3,667,246; 3,823,572; and 3,912,344.